Overspeed pitch lock



, March 1960 R. P. LAMBECK 2,928,477

OVERSPEED PITCH LOCK Filed June 14, 1956 2 Sheets-Sheet 1 INVE'N TOR RAYMOND F. LAMBECK BY Wm/M ATTORNEY March 15, 1960 R. P. LAMBECK OVERSPEED PITCH LOCK Filed June 14, 1956 FIG 2 FPOM awn/wen? g4 2 Shepts-Sheet 2 FIG. .3

FIG. 4

IN VE N TOR RA YMOND I? LAMBECK ATTORNEY OVERSPEED PITCH LOCK Raymond P. Lambeck, St. Petersburg, Fla., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application June 14, 1956, Serial No. 591,465

3 Claims. (Cl. 179-16021) This invention relates to variable pitch propellers and more particularly to mechanisms for locking the blades against pitch change.

It is an object of this invention to provide apropeller pitch lock which will prevent the blades from moving toward low pitch when a predetermined overspeed exists.

It is a further object of this invention to provide a pitch lock for fluid servo operated pitch changing mechanism wherein the fluid is trapped in one side of the servo motor when a predetermined overspeed condition is reached.

These and other objects of this invention will become readily apparent from the following detailed description of the drawings in which:

Fig. l is a partial cross-sectional view of a propeller hub with certain parts being shown schematically.

Fig. 2 is an enlarged detailed showing of the overspeed pitch lock valve.

Fig. 3 is an enlarged detailed showing of the centrifugally operated bleed valve, and

,Fig. 4 is an enlarged detailed showing of the surge valve.

Although pitch locks of various types are well-known in the art, most of these pitch locks require expensive heavy mechanisms whose weight and bulk cannot be tolerated in present day propeller requirements. Further more, these pitch locks operate on a principle involving the mechanical engagement of the blades. with a fixed hub portion to positively prevent movement of, the blades. According to this invention all these disadvantages are eliminated.

Referring to Fig. l, a propeller assembly is generally indicated at as having a hub 12. having a plurality of blade retaining sockets 14 in which are mounted one or more blades 16 for pitch changing movement relative thereto. A propeller dome 17 houses a main hydraulically operated pitch changing piston 18 which through cams 20 and 22 rotates a gear 24 which engages a gear segment 26 for varying the pitch of the blade 16. The pitch of the blades 16 is controlled by a governor schematically illustrated as dotted lines in the drawing. The flow of high pressure fluid from the reservoir 32 to either a low pitch line 34 or a high pitch line 36 both schematically illustrated as dotted lines in the drawing. The low pitch passage 38 communicates with the aft side of the pitch changing piston 18 while the high pitch passage 40 communicates with the front side of the piston 18 via an oil transfer tube 42. The governor control of pitch changing piston is more fully disclosed in U.S. Patent No. 2,402,065, issued June 11, 1946, to E. Martin.

When an increase in blade pitch is required, high pres sure fluid'is fed via the line 36 to the high pitch passage 40 then to the oil transfer tube 42 and then out to the forward side 44 of the main piston 18. On the other hand, movement of the blades toward low pitch is accomplished by directing high pressure fluidto the line 34, low pitch passage 38 and then to the aft side 46 of the pitchchanging piston 18.

Patented Mar. 15, 1960 In order to provide a circulation of fluid when the propeller blade is at a given operating pitch, at least one According to this. invention a centrifugally operated valve generally indicated at 60 is located in the nose of the propeller dome 17. The valve 60 comprises'a flyweight unit 62 (see also Fig. 2) and a valve element 64. The flyweight 62 during a predetermined overspeed will act on hearing plate 66. Bearing plate 66 compresses the spring 74. Spring 68 is preloaded and its length re- 'mains constant until the valve 64 is seated. The valve seal 70 engages with the seat 72. If the fiyweights 62 exert enough force on the bearing plate 66 to continue to force it to the right after the valve seats, then spring 68 will-be compressed. Spring 68 is primarily a lostmotion provision whose main value is shown by its operation during the reversing and feathering cycles of the. propeller. This operation is better described hereinafter. The propeller r.p.m. at which the flyweights will seat the valve seal 70 will depend on the capacity of the spring 74 and the number of adjusting shims 76 located in the assembly. I

-When a propeller overspeed is encountered, it is usual-: ly accompanied with a lack of sufficient pressure in the" transfer tube 42 and the chamber 44 on the front side of the piston 18 to overcome blade centrifugal twisting moment which tends to move the blades toward low pitch and the piston 18 forward or outboard. Under these conditions further movement of the blades towards a lower pitch will cause a further overspeed and possible damage to the propeller, power plant and airplane structure if not avoided. In order for the propeller blade 16 to go toward a further overspeed or lower pitch position, it is necessary for the main servo piston 18 to move in a forward or outboard direction. Since the chamber 44 at .the forward side of the piston 18 is filled with oil, a positive pitch lock can be obtained by preventing the oil in the chamber 44 from draining therefrom. Thus when an overspeed occurs the flyweights 62 are intended to urge the valve 64 to a position whereby the seal 70 engages the seat 72 thus preventing any further oil from draining from the chamber 44 and into the oil transfer tube 42. At the same time it is also necessary to close off the bleed between the forward side 44 and the aft side 46 of the main piston 18. As previously indicated, this bleed was provided by means of a valve 52 located in the cam roller 50. This valve is better illustrated in Fig. 3. Under normal operating conditions the valve element 52 is held in a downward position by'means of a spring 80 thereby permitting a passage of fluid from the'line 54 to the line 56 which connect both sides of the piston 18.

When a predetermined overspeed is encountered the valve element 52 by centrifugal force will move to the position shown so as to prevent passage of fluid from the line 54 toto the line 56. under pressure which is trapped in the forward side '44 of the piston 18 will flow to the line 54 and then through element 52 against its seat.

which the cam pitch lock valve element 64 operation. 1

In normal applications, it is planned to set valve 64 so that it will close at some r.p.m. below take-off r.p.m. The

At the same time fluid setting of spring 80 in the pitch lock action will occur. is done so that at the beginning of an overspeed, the mainoil flowfrom the propeller dome will. be. blocked off. and the'.r.p.m-.-will.. increaseat a relatively lower, rateuntil .the-bleedshu-twfif valve closes, finally lockingthe pitch... Thiszreducedrate.

of-Tapproach to the final lock pitch setting preventssovershooting-the. set r.p.m dueto. inertiaeffects. ItrrllSQ the, pilot, a little longer, period to. warn him. that: something. is going wrong.

The valve 64 is designed so. that. feathering the propeller. can be readily accomplished. even when .thervalvejs heldelosed. with the. flyweights. This 1 feature is. gained. I throughlhe spring.68.. If valve fi4 is held elosed liy the fiyw'eights, andifoil pressure is applied. at the-oiltransfc-n tube.;side. (right-handside) ofthe valve,,the valve 0311b? openedreadily by compressing spring- 68.. The oil pressure to. open thevalve is equal to the operating pressure (thatfistback pressure) on theleft-hand side. of. the. valve. plus .only a very small additional. amount needed tof compress. the spring; Thus, the operation'.of..the. pitch. lock valve will not act to prevent feathering; oij toaprevent bleed shut-off valvejwillidietermine the r.p.'rn. (above take-ofI' r.p.m.) at which full a the l fti he v insh ti u sh n s sure fluid will be fed to the aft side of the servo piston 18,

ie chamber 46, this fluid timibe available to flow into the slot 112 adjacent the attend of the oil transfer tube.

above-referred-to application.- Serial No.

lar lip 1 19"on;the:forward side: thereotiengagesmneof the flange like elements 9 .4 onthe, sleeve 92.. Eollowing. this and during movement off the servo piston 1'10-to the left the sleeve 92 is forced to the left thereby engaging the pitch lock valve element 64 so as to unseat this valve to permit fluid to. flow from. the chamber; 4.4 into; theioil theregaining ofnormal governing operation if. pressure...

ngainbecomes available in the oil transfertube.

clos,ed, they wil1 be held closed by thebackpressure. in. thermain dome chamber on thepoutboard side; of. piston 18.. This back pressure'of. coursecomes from: the I blade; centrifugal.twisting-momentsurgingthe bladesiowarddow: pitch. This is animportant feature and insures thatievenr.

thoughthepilot reduces the enginepowersetting or slows thezairplane down to bring the rpm. down to-a lo vi-r-ang e v thepitch .lockzwill remain'locked. It will remain locked-y until. either (a) adequate .oil pressureis appliedin the, oil. transfer tube42ito open valve 64, or (1;) virtuallyall.

r '25 Once an. overspeed occurs and valves 64. and 52; are

transfer tube: 42. 'I'hustheqhydraulic pitch lock isrphysie cally and mechanically disabled to permit:a reversing-10E:

the propellen a When the 'propeller. has reached;- its extreme-reverse 1 position it is desirable-to, reducejthe pressure. on the side ofthepitch changing piston 18', i.e.,chamber 46 to a..minimum. In. other; words; it; is; desiredttohave' only." sufficient. pressure; exerted onthe. back side; of. the pitch changing piston 18. to. keep it .in:.a full reversepositiomasr:

opposed to blade centrifugal twisting movement. Thus:- I although. themain'relief .valvemay. be; open in; the 800to backlpressure' disappears behind the two valves 64E andw 52, aswhen the propelleris stationary following; a feath.

eringmperation. With this feature, it will generally bepossible for the pilot to reduce the rpm; of an over:

speeding propeller. to a very moderate value-.byreducing. throttlesetting and slowing down the airp1ane= At this;v

r.p.m.,,the, drag of. thewiiidmilling propeller will;.b.e.-.lo.w v evemifthe feathering system. is disabled and. the propeller; cannot be feathered. Moreover, it is easier: to. get: the

propeller feathered if the windmilling is-very: low;

There'arecertain conditions otoperation .whentherpitchi lock willbeinan engaged'oractive position and' it-is de. sizable to, suddenly reduce the. pitch: ofsthe blades. Suchr acondition may. occur during take-offiwhere;mmalfunce 1( ).0O.p.s;i. range asurgezvalveis providedzwhichwill'open;

in appro timatelythe 500 p.s.i. range: 3To:.,tliis:'end;. at--; the. right-handend. of the. oil. transfenf. tube: 42, is. located a surge valve-generally: indicated at 120.. Thus asi betten seeminliig. 4,, a, valvesleeve122. is .iurged .;to the: right; by

a spring 124. In the positionshown passageLof. fluidxfrom;

the-line; 38; andthe port .1261 isiprevented from flowing. past the sleeve toward the passage: However; when: suffi cient:pressur'e;is;built;up in'thechamber 38 and on the aft ducing'thedifierential pressure acting on'the-piston: inturn relieves'thestresses: in thehub andprovidesonly sufficient pressure to maintain the blades in-a full reverse" tion: will" cause the hydraulic pitch: locks: tosengage;v and; themthepilot desires to, suddenly I'CVSISQ' lhBJZPiTOPGllEI'SilO;

, provides braking effect. Tothls. end ameans is:;p'rov ided;"-

for;mechanically-forcibly unseating'the valvegelement: 64.

.sosthat. thereis a. free flow; offiuid'from the-chamber? into the oihtransfer tube 42. The desiredlflowunder these; conditions is as shown by the arrowsin Fig. 2.

Returning,- however, to Fig. 1, the forwardend oflth'e' 1 oil transfer tube includes; a concentric; inner: sleeve .92:i. having-upstanding members 94 engagedby a spring; 96.... The members 94 are slidable in slots 95 atgthe upstream flIdiOfItllbC 42. Thespiing 96 holds the sleeve92 in the." position. shown so it is out of engagement: with the.valve=- element..64'. However, when a reversev position of.- the propeller. is: desired, it is necessary towithdraw the mechanicalpitch stop wedge 98 so that the stops 100 cam be-z retracted to a: position whereby the piston l8-isfree to.n1ove:to a forward position. 'Normally'the stop;100

wouldjgbe engaged by the sleeves itllcarriedby the piston 18; 1 The: operation. of these mechanical low. pitch stops:

issmore clearly. illustratedv in. US. patentapplication. No. 413,188.,1fil6d:M8l1Ch 1,.1954,.by.R. P. .IJarnheck; now:U.S. Patent No. 2,843,212 issued July 15,1958.

Ingorder to i remove: the. wedge:- 98; from the: position strewn, ,it.'is; necessary to; move. the. servozpistomlltlitoai side of the pitch changing piston 18, pressure will build upin the chamber: 130. so thatxpressureswill act on the difierential;area;:1$2 Ofjthe sleeve 122 to force it toward the left e againstthepressure of spring 124: to permit freepassage- 1 of fluid, frompassagerSS; port 126. and then to. port 40.

This-in; reality drains; fluid? from one side of r the pitch changing piston 18. to. the. opposite side thereof thereby re-- position;

efficientipitch lock mechanism has 'been"providedwherehy the safety: of pitch loclc operatiom is obtainedwitli a very; slight increase in: the cost: of productionpropellersw Furthermore, propellers: already in use: can lie-simply modified with a minimum of cost and extra parts? Furthermore, aj-pitchT lockhas: been: provided which is't ver-y'light andparticularly' small) as compared with the bulky mechanical pitch "locks-- known heretofore.

Although only one embodiment of this invention has been illustrated andde'scribed herein; it will be apparent that various changes and modifications can bemade in the construction and arrangement of the various parts" without'departi'ng; from the scope. of: this" novel' concept.

.What iris-desired-by'LettersPatent' is: A V

1."In"a propeller having: aihub, a plurality of bladesmounted for pitch changing movement. 'relativetliereto a hydraulic pitchichangingjservo motor mounted, in said huh. and; operativetov vary; the. pitch of. said. blades, a;

source. of fluid. under. pressure anda drain, afirsttspeed; responsive. means :forconnecting; either one sideof. said: moton'to. said source-and the; other; to; drain,-to..control. said. servo moton-goyerspeed .ltesponsivemeans carried.:by: said: huhtfbrtblockingtthe =:connection:.of: onlymner sidei said servo with said first speedmesponsiveameansumeawc As. a. result of? this: invention, a simple yet highlyproviding a bleed between one side of said motor and the'other, and means for automatically closing said bleed. 2. In a propeller having variable pitch blades, means for varying the pitch of said blades including a servo motor having two operative sides, means conducting high pressure fluid to either of said sides of said servo motor for controlling said servo motor, said controlling means including a speed governor providing increase pitch and decrease pitch control signals, means responsive to a predetermined rotational overspeed condition of said propeller for trapping high pressure fluid in one of said sides regardless of the control signal of said speed governor, a bleed from one side of said motor to the other, and overspeed responsive means for closing and opening sai bleed.

3. In apropeller having a hub, a plurality of blades mounted for pitch changing movement relative thereto, a hydraulic pitch changing servo motor mounted in said hub and operative to vary the pitch of said blades, 9. source of fluid under pressure and a drain, a first speed responsive means for connecting either side of said motor to said source and the other to drain to control said servo motor, overspeed responsive means carried by said hub for blocking the connection of only one side of said servo with said first speed responsive means, means providing a bleed between oneside of said motor and the other, and a second speed responsive means for automatically closing said bleed.

References Cited in the file of this patent UNITED STATES PATENTS Van Alstyne Oct. 7, 1958 

